In the processing of gas, oil or kerosene to other petrochemicals, the liquid is fed into piping which passes through a heated furnace and exits as a gas. The piping in the furnace typically is tortuously arranged in a vertical plane and supported from the roof of the furnace. One or more temperature sensing devices are used to sense the temperature of the fluids in the pipes for regulation of the input temperature of the fluid and the rate of flow of fluids through the pipe. Heretofore, the temperature sensing device or thermowell has typically consisted of a tube with a closed end where the closed end is inserted through a hole in a return bend of the pipe or furnace tube and welded in place so that the closed end tip of the tube extends approximately to a center point of the internal diameter of the pipe. An electrical thermocouple is then inserted into the tube for sensing temperature. The thermocouple consists of two wires of dissimilar metals in a ceramic sheath and covered by a high alloy metal sheath. The tube provides a housing to protect the thermocouple from damage in the high temperature environment.
One of the problems involved with temperature sensing devices or thermowells is their replacement with respect to the piping after a considerable period of usage. As a practical matter, replacement of the temperature sensing device should be as simple as possible so that repair and costs are reduced or minimized.